Glasses of varying compositions particularly for use in optical and ophthalmic applications are known. Such glasses have, for example, a refractive index of about 1.7, an Abbe number of about 35, and a density of about 3.2. These glasses exhibit good resistance to acids and viscosities at the liquidus in excess of 22 Pa·s, which is advantageous for their production, allowing for direct molding. These properties make such glasses particularly suited for optic and ophthalmic applications. However, such glasses may have low viscosity at the liquidus temperature, low chemical durability, yellow coloration and/or may be associated with high batch costs.
Furthermore, these glasses are often formed using manufacturing processes that employ arsenic (As2O3) as a fining agent. As2O3 is a very effective high temperature fining agent which allows for O2 release from a glass melt at high melting temperatures and minimizes the creation of compositional inhomogeneities and gaseous inclusions in the glass product. However, the use of As2O3 poses health and environmental hazards and requires special handling during the glass manufacturing process.